In early October 1862, Abraham Lincoln received a letter from God. "I am your Heavenly Father and the God of all Nations," it began. God had particular explanations and instructions for the president, whose entire term of office had been defined by war. "I am the cause for the disruption between the North and the South," he continued, and the point was to destroy the "horrible state of affairs" that man's "selfish nature" had brought. "I am not partial and have no respect of persons." Coming just weeks after the preliminary Emancipation Proclamation, the letter made it clear that God wanted to destroy slavery. For further instructions, God told Lincoln to gather six of his best men and meet in person "my instrument the Messenger of Peace the Christ of this day." Conveniently, the "Christ of this day" was not only staying in Washington, but lived just a few miles from the White House, at 476 Pennsylvania Avenue. At the meeting and through the medium, God would explain "what to do that will speedily terminate this Devilish war."Lincoln did not believe the letter was from God, of course; as he suspected, it came from a local religious devotee named Lydia Smith, who believed herself to be God's medium. For Lincoln, this kind of supernatural penetration was lunacy, not prophecy. He didn't believe that God walked the earth, inserting himself into the affairs of men. He told one group of ministers who had earlier pressed him for emancipation that these were not "the days of miracles," and that "I suppose it will be granted that I am not to expect a direct revelation."Yet for as much as Lincoln disclaimed the possibilities of "direct revelation," writers to him thought otherwise. This was, after all, the mid-19th century, when religious fervor ran deep in the country's psyche, not to mention the middle of the Civil War. The possibility of overturning slavery had so fired spiritual sentiments across the North that self-proclaimed mediums and prophets believed that God was on the move in the nation. Throughout the war, and especially when it came to emancipation, people sent the president missives on what God was doing, where Jesus was and how the sacred could win the war for the Union. Perhaps the most interesting spiritual letter Lincoln received was from a man named George F. Kelly. A month after the Emancipation Proclamation went into effect in 1863, Kelly warned the president that he was "surrounded by Spies and men of evil intentions." Perhaps, he wrote, Lincoln wondered now "if God has forsaken us." But, Kelly insisted, this was not the case. Instead, God had further demands for the president. Kelly, claiming to be channeling God, called on the president to "adopt the plans called, Radical," which would emancipate the slaves and bring full racial equality to the nation. "I have Seen in visions," Kelly went on. The son of God, he reported, had returned and was ready to lead Lincoln's military to overthrow the South. "Have not the honest hearted been longing for the Second 'Jesus' to Save this nation and the world," Kelly asked, and then answered, "Have ye not heard that in one of the New England States 'God has raised him up in humble life'?" Did he not, Kelly asked, "do even So with His former Servant; who toiled with the people more than thirty years?" Kelly's prophetic vision concluded that in two weeks, Jesus would reveal himself and win the war for the Union.Although Lincoln considered Kelly a "Crazy Man," as the president wrote on one envelope from him, the letter was telling. In the midst of a war where white men were killing white men in epic numbers over, in part, the institution of slavery, Kelly now envisioned Jesus to be a New Englander who would fight to free the black captives. In Kelly's eyes, Jesus looked and sounded awfully similar to John Brown. The man who had been executed for treason only a few years earlier, but who had fired spiritual sentiments himself with comparisons to Christ, seemed to be reincarnated and ready to fight.There were other letters Lincoln received from other spiritual guides, and there were other claims about Christ's power in America at the time. Some demanded money, as was the case where one writer requested half a billion dollars to "Reveale, Christ, Jesus." At first glance, such letters, and the millenarian spirituality they articulated, sound like vestiges of the culture modern men and women left behind. We would expect talk of revelations and prophecies from colonial Puritans, who executed one another with threats of witchcraft. But the mid-19th century was hardly the modern secular society we sometimes imagine it to be. Firsthand encounters with the sacred were commonplace claims by even respected, "modern" Americans.Lincoln may have considered George Kelly and the others "crazy" for their visions, but their experiences were little different from those of the abolitionist and feminist Sojourner Truth, who met with Lincoln in October 1864 and bonded with him over one of his favorite Bibles. Years earlier, Truth believed that God spoke to her. According to one of Truth's friends, she said that "God revealed himself to her, with all the suddenness of flash of lightning."Experiences like this one led Truth to join the growing Millerite movement of the 1830s, which followed the biblical calculus of William Miller toward the conclusion that Jesus was going to return in the early 1840s. When the Second Coming failed to materialize in 1844, the "Great Disappointment" left many confused. But Truth continued to believe that God and Christ could and would intervene in this world; when her fellow abolitionist Frederick Douglass spoke despairingly about the chances for justice, she interrupted him with a rebuke in the form of a question, "Frederick, is God dead?" There was no disappointment for Joseph Smith, for whom Jesus and God were very much alive. He met with them in upstate New York around the same time Sojourner Truth was earning her freedom, and Smith's "first vision" became a central element of Mormon theology and belief. Indeed, the notion that God still intervened in this world was critical to the emergence of the Church of Jesus Christ of Latter-day Saints, and during the Civil War, many Mormons believed that the carnage was evidence of Smith's prophetic powers. In 1832, he had prophesied that "war will be poured out." It would begin with South Carolina and envelop the entire nation. "For behold, the Southern States shall be divided against the Northern States." Nat Turner's spirit would take over, and "after many days, slaves shall rise up against their masters, who shall be marshaled and disciplined for war." At the time of Lincoln's election, one Mormon diarist wrote excitedly, "The south is angry; the North is no better and from what I can see they are both hastening to fulfill the Prophecy of Joseph Smith Jr."If we broaden our scope even further, we see that during the Civil War, more and more Northerners were searching for God's voice amid the chaos and carnage. Almost as quickly as the war began, some Northerners were pushing for the phrase "In God We Trust" to be placed on coinage. In 1864, a group of Protestant clergy formed the National Reform Association to petition Lincoln and Congress to amend the Constitution to acknowledge "Almighty God" and "the Lord Jesus Christ as the Ruler among nations." Perhaps most famously, Julia Ward Howe imagined the spirit of Christ (who was "born across the sea") inspiring soldiers in this country. "As he died to make men holy," the "Battle Hymn of the Republic" versed, "let us die to make men free." In the decades after the war and into the 20th century, the song became a staple of American religious culture. Its most famous vocalists, in fact, have been the members of the Mormon Tabernacle Choir.And of course, by the war's end it was Abraham Lincoln himself who was ruminating on the spiritual meaning of the war and slavery, almost as much as the prophets and mediums who had previously written to him. During his now famous Second Inaugural on March 4, 1865, Lincoln made public his private wonders about what God was doing. He asked his audience, what caused the war? What were God's purposes for the future? Lincoln was uncertain on much of it, but he knew this: slavery was somehow the cause of the war; God hates injustice; and the nation must now bring "charity" and "right" to heal the land. Beyond that, he concluded, "The Almighty has His own purposes."When Lincoln invoked the Almighty during his Second Inaugural, he tapped into the widespread sense in the North that something spiritual was happening during the war. For as much as he differed from people like George Kelly and Lydia Smith, he shared with them the focus on trying to discern what God had in store for the land. Some believed that the events of the war were so momentous that they were themselves evidence of the work of Jesus and God on earth. Others hoped that by invoking the sacred - either through song or in the Constitution - they could gain the Almighty's favor or empower men to continue to fight.The songs, the letters, the prophecies, the experiences spoke to another layer of how deeply the Civil War and emancipation touched hearts, minds, and spirits of Americans in the North. Deluged in blood, but hopeful for a peaceful nation shorn of enslavement, these mystics, mediums, prophets, politicians, writers and clergy believed that the events of 150 years ago had ushered in God's intervention. They demonstrate most clearly how war changes people not only in body, but in soul, too.Follow Disunion at twitter.com/NYTcivilwar or join us on Facebook.Edward J. Blum, a historian at San Diego State University, and Paul Harvey, a professor of history at the University of Colorado at Colorado Springs, are the co-authors of "The Color of Christ: The Son of God and the Saga of Race in America."